1. Field of the Invention
The invention relates to a collision detection apparatus.
2. Description of the Related Art
Conventionally, a technique for protecting a pedestrian, a bicycle, a bike and the like has been reported that lowers a threshold value for determining whether or not it is necessary to operate a pedestrian air bag against an impact force as a result of determining that a risk of collision is high when an obstacle detected in a periphery of a vehicle is a pedestrian or the like (e.g. Japanese Laid-open Patent Publication No. 2003-291758).
Incidentally, in the impact forces detected at the time of collision with a bicycle being operated by a bicycle rider, the impact force at the time of collision with a side surface of a pedestrian or a bicycle being operated by a bicycle rider becomes larger than the impact force at the time of collision with a front surface or a rear surface of the bicycle. For example, as illustrated in FIG. 1, this is because that although a pressure sensor used as a collision detection sensor measures the effective mass of a collision object, at the time of the collision with the front or rear surface of the bicycle being operated by the bicycle rider, the bicycle rider is separated from the bicycle just after the collision with a front bumper of a vehicle and, therefore, the pressure sensor can measure only the effective mass of the bicycle alone. Consequently, the output value from the collision detection sensor becomes low.
Thus, when a threshold value at the time of prediction of collision with the pedestrian or the bicycle being operated by the bicycle rider is set to a value corresponding to the collision with the pedestrian or the collision with the side surface of the bicycle, the threshold value becomes higher than the impact force assumed at the time of collision with the front surface or the rear surface of the bicycle. Therefore, in that case, it may be possible that the collision with the front surface or the rear surface of the bicycle being operated by the bicycle rider cannot be detected. Further, when a threshold value that corresponds to the collision with the front surface or the rear surface of the bicycle is previously set, the threshold value becomes excessively lower in comparison with the impact force generated by the collision with the pedestrian or the side surface of the bicycle. Thus, in that case, a possibility of erroneously detecting an obstacle, which is not a target to be detected, as an object to be detected, which is set for the purpose of protecting a person outside of the vehicle, such as a pedestrian and a bicycle rider.
There is a need for a collision detection apparatus capable of increasing the possibility of detecting collision t with a front surface or a rear surface of a bicycle being operated by a bicycle rider while decreasing the possibility of erroneously detecting an obstacle that is not an object to be detected as the object to be detected when the collision with an obstacle outside of a vehicle has been detected.